Japan Regulators Stumped by 787 Battery

By

Yoree Koh And

Yoshio Takahashi

Feb. 5, 2013 6:50 a.m. ET

TOKYO—Japanese aviation regulators remain stumped over the root cause of the battery incident that led to the world-wide grounding of the Boeing Co. 787 Dreamliner jet, echoing the apparent lack of progress made by their U.S. counterparts several weeks into their respective investigations.

The Japan Transport Safety Board said Tuesday that computed-tomography scans revealed the extent of damage to the powerful lithium-ion battery. But the scans offered few useful clues on what caused the battery to overheat. That has led...